Direct anterior composite restorative resins, in conjunction with the acid etch technique, are used extensively in clinical dentistry. The bonding of composite resins to etched enamel is mechanical in nature. The curing resin penetrates the microspaces produced in the enamel by acid etching. The composite restorative resins are viscous because of their high inorganic filler content. Intermediary low viscosity resins were introduced for use on etched enamel surfaces prior to the placement of composite resins because it was reasoned that low viscosity resins would penetrate deeper into the etched enamel surfaces and thus ensure intimate interfacial contact between the resin and enamel. The influence of low viscosity bonding resins have been evaluated in numerous in vitro studies in which bond strength, resin penetration and microleakage were determined. The results of these studies are contradictory. No clinical studies have been carried out. The purpose of this clinical study is to evaluate the effect of a low viscosity bonding resin on the composite resin - tooth interface. One hundred patients attending the University of Alabama School of Dentistry with at least two Class V lesions located on the anterior or premolar teeth will be selected for this study. One randomly selected lesion will be restored with a conventional composite resin after acid etching while a low viscosity bonding resin will be applied to the etched enamel surfaces prior to the restoration of the other lesion with the composite resin. The patients will be recalled after 6, 12 and 18 months and the color match, cavosurface marginal discoloration, anatomic form and caries will be evaluated by two evaluators standardized in the use of these criteria. Scanning electron microscopy of replicas of the restorations will be used to evaluate marginal adaptation. The rating scales as recommended by a Working Group of the Commission on Dental Materials, Instruments, Equipment and Therapeutics of the Federation Dentaire Internationale will be used in this proposed study. All tests for statistical significance will be completed at the 5 percent level of significance.